Pulverizer



Aug. 9, 1938. E. G. BAILEY ET AL PULVERI ZER Filed March 23, 1934 57 Erv/n G. Bai/e w ymw g d r Y. a E Y M m T MW M V: B

Patented Aug. 9, 1938 UNITED STATES PATENT OFFICE PULVERIZER Application March 23,

4 Claims.

Our present invention relates to apparatus for pulverizing materials, such as coal, cement, rock products and ore, and more particularly to pulverizers wherein the material to be pulverized 5 passes through a plurality of successive grinding stages, each formed by a pair of Vertically spaced relatively rotatable grinding rings between which is positioned an orbital row of rolling grinding elements. In operation the grinding elements move over the surface of the grinding rings and eifect a grinding action on any material between the contacting surfaces. When the relative movement between the grinding parts is produced by having the lower grinding ring rotary and the upper grinding ring non-rotary, the material undergoing pulverization is advantageously supplied to the inner side of the row of grinding elements and passed outwardly therethrough. The outward flow of material may be partly due to a head of material at the inner side ofthe row, but is mainly due to the centrifugal effect exerted on the material by the rotation of the lower grinding ring, over the upper surface of which the material passes, and the grinding elements, and to the displacement effect of the rolling grinding elements on some of the material in their path of rotation. At economical speeds, the combined effects normally result in a too rapid flow of material across the grinding area.

In a multi-stage pulverizer, in which the grinding stages are vertically spaced and formed by top, intermediate and bottom grinding rings between the successive pairs of which are respectively positioned upper and lower circular rows of metallic grinding balls having a relative rotation with respect to the grinding rings contacting therewith due to a floating drive connection to the intermediate ring, the material passes outwardly through the upper grindingv stage and inwardly through the lower stage; The material tends to pass at a higher speed through the upper grinding stage due to the centrifugal force imposed thereon in that stage, while the centrifugal effect, if any, on the material in the low- 45. er stage will oppose its passage therethrough. The depth of material in a grinding stage of the character described is an important factor affecting the amount of grinding accomplished therein, as little, if any, grinding will be done on the upper ring of the stage if the depth of material falls below a certain value. Thus with a too rapid flow of material throughthe upper grinding stage, those grinding parts will do less grinding than they are capable of doing, while the 55 lower grinding stage will be loaded beyond its 1934, Serial No. 716,936

grinding capacity. This undesirable distribution of the grinding load naturally results in a decrease in the degree of fineness of the product. As pulverizers of the character described are normally associated with classifying apparatus for separating and returning the coarse particles to the pulverizer, the amount of coarse particles returned correspondingly increases, with a corresponding increase in the cost of grinding per ton of product of the desired degree of fineness.

The rate of passage of the material through the upper grinding stage, and thereby the depth of material therein and the amount of the circulating load, may be controlled by providing flow restricting means at the outer or discharge side of the upper grinding stage, as disclosed, for example, in, our prior joint patent with Perry R.

Cassidy, No. 2,071,379.

Heretofore, as shown in our said prior patent, such flow controlling provisions have consisted of an annular basket or plate forming a restricted annular gap with the rotary intermediate ring in the path of flow of the material passing from the upper grinding stage to the lower stage. Such means have been found objectionable because of their inherent inability to maintain a uniform fiow controlling effect for an extended period of operation and the tendency of the material to pack at the gap. This lack of'uniformity of control is mainly due to changes in position of the intermediate ring relative to the gap forming provisions with wearing of the lower grinding ring and balls and Wear on the gap-defining edge of the basket or ledge plate due to friction of the material, which is increased by the rotation of the adjacent intermediate ring. The variations in size of the flow controlling gap due to these various causes may be somewhat offset by readjusting the position of the gap-forming provisions. The proper adjustment however cannot be accurately determined without interrupting the operation of the pulverizer, and moreover is limited in extent.

The general object of the present invention is the provision of pulverizers of the character described with improved provisions for controlling the flow therein of material undergoing pulverization. A more specific object is the provision of pulverizer flow controlling means which will maintain a uniform flow controlling effect regardless of changes in size or position of the grinding parts and are not subjected to undue wear in operation. A further specific object is theprovision of a fiow controlling dam on a pulverizer rotary grinding ring having an outward flow of material thereon so constructed and arranged relative to the grinding area on the ring to substantially neutralize the centrifugal effect thereof on the material undergoing pulverization. A further specific object is the provision of a multi-stage air-swept pulverizer of the general character described having a flow controlling dam on the intermediate rotary ring thereof associated with means for facilitating the separation of fines before the material reaches the classifier.

The various features of novelty which charac' terize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which we have lustrated and described various embodiments of our invention.

Of the drawing:

Fig. l is a sectional elevation of a gravity discharge pulverizer incorporating our invention;

Fig. 2 is an elevation and Fig. 3 is a plan view of the adjustable skirt shown in Fig. 1; and

Fig. 4 is a fragmentary view illustrating a modified dam construction.

The gravity-discharge type pulverizer illustrated in Fig. 1 comprises a metallic casing 30 .having a cylindrical upper section enclosing the material pulverizing parts which include a nonrotary top grinding ring 3], a rotary intermediate grinding ring 32, and a non-rotary bottom grind ing ring 33 spaced vertically in the casing, a circular row of rolling grinding elements, preferably in the form of heavy metallic balls 34, between the top and intermediate grinding rings and a concentric row of grinding balls 35 between the intermediate and bottom grinding rings. A floating drive connection for the intermediate grinding ring from a main drive shaft 36 axially arranged relative to the ball rows is effected through a drive yoke 37 mounted on the upper end of the drive shaft and having driving arms' 38 thereon each positioned between andvertically movable relative to a pair of plates 39 on the inner side of the intermediate grinding ring. Similar parts provide a floating non-rotary connection between the top grinding ring and the casing 30, as shown. The adjacent faces of the several grinding rings are formed with races or tracks along which the corresponding rows of balls move. A substantial grinding pressure is ordinarily applied to the upper side of the top grinding ring 3| by a series of helical pressure springs 46 arranged in a circular row on the top grinding ring, as indicated in Fig. l. The spring pressure is externally adjusted in accordance with the hardness of the material undergoing pulverization. The material to be pulverized is delivered to the upper part of the casing through one or more feed spouts 42 projecting through the casing top plate 4|.

The feed spouts 42 deliver the material centrally of the top grinding ring, Whereit is directed to the inner side of the upper row of balls 34 by a conical cover plate 43 mounted on the intermediate grinding ring. The material will pass substantially spirally outward on the inter -mediate grinding ring and through the upper row of balls, and is pulverized thereby. The material pulverized in the upper grinding stage drops to the outer side of the lower row of grinding balls. The partly pulverized material drop- ;ping to the lower'grinding stage is fed by gravity inwardly through the lower row of balls 35. The material is further ground in the lower grinding stage and drops from the inner side of the lower row of balls into the lower or discharge section of the casing, to which a discharge conduit 45 is connected. The discharge of the material is facilitated by a series of sweep blades 46 mounted on the drive yoke 31.

In accordance with our present invention, desirable grinding conditions are continuously maintained in each grinding stage with high capacity operation and low power consumption by employing flow controlling or load distributing provisions which are constructed and arranged to function uniformly in operation over a prolonged period.

One of the novel features of our flow controlling provisions is their arrangement on and rotatable with the intermediate ring 32, whereby the troubles heretofore due to wear on the stationary ledge plate in proximity to the rotary ring will be eliminated. In the drawing we have illustrated various forms of flow controlling provisions of this type.

The flow control provisions consist of means forming an adjustable dam on the periphery of the rotary intermediate ring 32, and are based upon our theory that there is a slope corresponding to the speed of the intermediate ring and coefiicient of friction of the material undergoing pulverization, on which the particles of material will be in equilibrium with the component forces of gravity and friction balancing the component of centrifugal force. Under such conditions, the flow of material over the top of the dam will be due to the push or displacing effect thereon of the balls 34 and the discharge of material will increase as the level in the grinding zone tends to build up.

If the dam slope be too low the material will flow at too great a rate, and if too high the material will be retained in the top ring for too long a period, and thereby lower the capacity, increase the power consumption of the pulverizer, and throw an excessive amount of the grinding load on the upper row of balls tending to cause the material to pack therein.

In the construction illustrated in Figs. 1 to 3, the dam is formed by a cylindrical ledge plate 57 mounted on the periphery of the intermediate ring and carrying an adjustable skirt section 58 formed by a plurality of overlapping curved plates 59, each of which is provided with vertically elongated slots 69 through which project bolts 6| carried by the ledge plate 51. justable skirt section is held in any of its positions within its range of adjustment by curved washers 62 and nuts 63 carried by the bolts. The raising or lowering of the skirt correspondingly varies the effective angle of the dam relative to the grinding race. With this arrangement The ada ledge plate of a height corresponding to the minimum angle calculated may be mounted on the intermediate ring and the most desirable angle within that range determined experimentally by varying the height of the skirt. Small variations in the height of the dam have been found to cause substantial variations in the pulverizer capacity, fineness-of the output, and power consumption. For example, an increase in height of the dam of approximately two inches was found to substantially lower the capacity and fineness of the product and increase the power consumption 40% as compared with the results obtained with the lower height.

The 1.:

cylindrical ledge plate 51 may be detachably mounted on the grinding ring, as in Figs. 1 to 3, or integrally formed thereon as shown in Fig. 4.

With the various forms of flow controlling pro visions disclosed, the pulverizing load will be de-.

sirably distributed so that under varying load conditions, the depth of material in the upper grinding stage will remain substantially the same. By this arrangement, a substantially uniform. and predetermined grinding effect will be given to the material in the upper grinding stage, and a further grinding supplied in the lower stage. The grinding load in the several stages can be thus proportioned so that none of the stages will be overloaded with a consequent decrease in the degree of fineness of the product and increase in circulating load, or underloaded with a consequent decrease in pulverizer capacity and increased wearing or the grinding parts.

While in accordance with the provisions of the statutes we have illustrated and described herein the best forms of our invention known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of our invention may sometimes be used to advantage without a corresponding use of other features.

We claim:

1. A pulverizer comprising a casing having an inlet for material to be ground and an outlet for ground material, a grinding stage having an outward fiow of material therethrough and including an upper grinding ring, a rotary lower grinding ring movable relative thereto, and an orbital row of rolling grinding elements positioned between said grinding rings, means for supplying material to be ground to the inner side of said row of elements, means forming an annular dam, on said rotary grinding ring at the outer side of and extending above the centers of the elements in said row, said dam being radially spaced throughout its height from said row of elements, and means for varying the effective height of said dam to regulate the discharge and fineness of the material leaving said grinding stage including a sectional skirt forming the upper portion of said dam, and means for varying the position of said skirt.

2. A pulverizer comprising a casing having an inlet for material to be ground and an outlet for ground material, a grinding stage having an outward fiow of material therethrough and including an upper grinding ring, a rotary lower grinding ring movable relative thereto, and an orbital row of rolling grinding elements positioned between and contacting with said grinding rings, means for supplying material to be ground to the inner side of said row of elements, a circular ledge plate on the periphery of said rotary grinding ring forming a circumferential dam on said rotary grinding ring at the outer side of and radially spaced throughout its height from said row of elements, and means for varying the height of said dam to regulate the amount and fineness of the material discharging from said grinding stage including an upper skirt section adjustably mounted on said ledge plate.

3. In a pulverizer comprising a casing having an inlet for material to be ground and an outlet for ground material, an upper grinding stage having an outward flow of material therethrough and including a rotary grinding ring and an orbital row of rolling grinding elements positioned thereon, a lower grinding stage receiving material discharging from said upper grinding stage, means for supplying material to be ground to the inner side of said row of elements, an adjustable flow controlling dam mounted on said rotary grinding ring at the outer side of and radially spaced throughout its height from said row of elements, and means for varying the effective height of said dam for regulating the amount and fineness of the material delivered to said lower grinding stage including a sectional skirt forming the upper portion of said dam, and means for varying the position of said skirt.

4. In a pulverizer comprising a casing having an inlet for material to be ground and an outlet for ground material, an upper grinding stage having an outward fiow of material therethrough and including a non-rotary top grinding ring, a rotary intermediate grinding ring movable relative thereto, and an orbital row of rolling grinding elements positioned between said top and intermediate grinding rings, a lower grinding stage receiving material discharging from said upper grinding stage and having an inward flow of material therethrough and including said rotary intermediate grinding ring, a non-rotary bottom grinding ring, and an orbital row of rolling grinding elements positioned between said intermediate and bottom grinding rings, means for supplying material to be ground to the inner side of said upper row of elements, a circular ledge plate on the periphery of said rotary grinding ring form ing a circumferential dam on said intermediate grinding ring at the outer side of and radially spaced throughout its height from said upper row of elements, and means for varying the height of said dam to regulate the amount and fineness of the material delivered to said lower grinding stage including an upper skirt section adjustably mounted on said ledge plate.

ERVIN G. BAILEY. RALPH M. HARDG'ROVE. 

